PROJECTSUMMARY Pulmonary hypertension(PH)ischaracterizedbyprogressivepulmonaryvascularremodelingthatleads to exertional dyspnea, severe hypoxemia, and ultimately to right heart failure and death.For patients with PH and significant remodeling, treatment options are limited and new therapies urgently needed. This proposal examines a novel mechanobiological feedback mechanism involving signaling by YAP (Yes-associated protein)andTAZ(transcriptionalco-activatorwithPDZ-bindingmotif)thatmaybecriticalinPHdevelopment. Pulmonary artery (PA) stiffness causes right ventricular stress and is associated with increased PH mortality.UtilizingatomicforcemicroscopyonPHlungslices,Dr.DieffenbachhasdemonstratedincreasedPA stiffnessatthecellularlevelinhumanPHandearlylocalarterialstiffeninginrodentPHmodels.Furthermore, increased matrix stiffness drives remodeling phenotypes in pulmonary artery smooth muscle cells and endothelial cells, indicating that PA stiffness itself can fundamentally bias cells towards pathologic behaviors. Dr. Dieffenbach has recently found that stiffness-dependent phenotypes require signaling by YAP and TAZ, transcriptional modifiers activated by mechanical stress. These data led to the hypothesis that YAP and TAZ arekeysensorsofthePAlocalmechanicalmicroenvironmentanddriversofpathologicarterialremodeling. This investigation focuses on the scope and mechanism of microenvironment-driven YAP/TAZ activation, andfurthermorewhetherYAP/TAZinhibitioncanarrestorreversevascularremodelinginvivo.Inthefirstaim, Dr. Dieffenbach will use cutting-edge bioengineering techniques to investigate microenvironment-driven remodeling phenotypes and their dependence on intact YAP/TAZ signaling. In the second aim, he will study specific downstream mechanisms that mediate the pro-remodeling effects of YAP/TAZ mechanoactivation. Finally,inthethirdaim,hewilldeterminetheimpactofinhibitingYAP/TAZactivityinvivoinrodentPHmodels. This research will be performed at Brigham and Women?s Hospital, a core teaching hospital of Harvard MedicalSchool,andattheHarvardSchoolofPublicHealth.Dr.Dieffenbachwillworkunderthementorshipof Dr.Fredenburgh,anexpertinpulmonaryvascularbiologyandpulmonarydiseasemodeling,andDr.Fredberg, an expert in bioengineering, cellular dynamics, and mechanobiology. With the guidance of his mentors and scientificadvisorycommittee,Dr.Dieffenbachhasdevelopedacomprehensivefive-yeartrainingprogramthat includes mentored research, didactic coursework, seminars, presentations at scientific meetings, manuscript preparation,andfuturegrantplanning.Dr.Dieffenbachisdedicatedtoacareerinacademicmedicine,withthe long-termgoalofbecomingaclinician-scientiststudyinglungdiseasesdrivenbyalterationsinthemechanical microenvironment. The research and career development outlined in this award will allow Dr. Dieffenbach to developtheskillsneededtolaunchanindependentcareerinthemechanobiologyofpulmonarydisease.